Four Spikes

Exact details of Christ's crucifixion were clearly illustrated before the event happened. Only a Being who transcends time could do that.
Some painted depictions with heels to the sides of the crucifix upright are Giovanni Tiepolo's "The Lamentation at the Foot of the Cross", Rembrandt van Rijn's "The Raising of the Cross" and inside Answers in Genesis's Ark Encounter exhibit. https://answersingenesis.org/ministry-news/creation-museum/depicting-crucifixion-jesus-christ/